D.C. Code § 39-102

In order to make the said library an effective supplement of the public educational system of the said District and to furnish the system of branch libraries provided for in § 39-101, the Board of Library Trustees, hereinafter provided, is authorized to enter into agreements with the Board of Education of the said District for the establishment and maintenance of branch libraries in suitable rooms in such public-school buildings of the said District as will supplement the central library and branch libraries in separate buildings. The Board of Library Trustees, hereinafter provided, is authorized within the limits of appropriations first made therefor, to rent suitable buildings or parts of buildings for use as branch libraries and distributing stations.